Investigators probing Michael Schumacher's accident have ruled out faulty skis, inadequate signage and excessive speed as possible causes of his life-threatening off-piste fall in the French Alps last month.

They said signs marking the edge of the piste Schumacher skied off just before the accident on December 29 were in line with legal requirements, his rented skis were in perfect condition, and that the Formula One legend had appeared in control of his speed.

The seven-time world champion has been in a medically induced coma since he fell on an off-piste section between two regular slopes in the ski resort of Meribel and slammed his head on a rock, prompting his evacuation to a hospital in the city of Grenoble.

Investigators are seeking to determine why the accident happened, and whether anyone - the resort, the ski rental shop, Schumacher himself - is at fault.

Patrick Quincy, the prosecutor in charge of the probe, told a press conference that rules determining how to mark the edges of ski slopes in France had been "respected" and that the racing driver had deliberately skied into the off-piste area.

The skis, meanwhile, were "not the cause of the accident" and the bindings were "in good condition", said Stephane Bozon, one of the policemen involved in the probe, following speculation a safety release on Schumacher's skis did not operate properly.

He was skiing "at a completely normal speed for this type of terrain and for a good skier," Bozon added at the press conference in Albertville, not far from Grenoble.

Much has been said about a camera that Schumacher had strapped onto his helmet at the time of the accident, and investigators said they had been able to retrieve the footage and look at it.

Schumacher's manager, Sabine Kehm, had denied last week that he was skiing fast "because it appears he helped a friend who had just fallen".

Mr Quincy said the footage on the camera lasted only two minutes, but that the racer cannot be seen helping anyone.

A flight attendant had also claimed to have inadvertently caught Schumacher's fall on his smartphone while he filmed his girlfriend on the slopes, and pledged to hand the video over to police, German news magazine Der Spiegel reported.

But Mr Quincy said investigators had so far not received any such footage and that he was "doubtful" of the claim.

Schumacher appears to have skied on a partially covered rock, lost his balance and fallen on another rock further down, he added.

The impact was so strong it split his helmet in two.

The accident has shocked Schumacher's legions of fans and devastated his wife Corinna and two teenage children.

Scores of reporters, television crews and photographers have descended on the hospital in Grenoble, putting pressure on staff as the establishment tries to deal with the impact of having a famous patient.

On Tuesday, Corinna Schumacher pleaded with the media to leave her family and the doctors alone.

Schumacher dominated Formula One before retiring in 2012, winning more titles than any other driver and enjoying 91 Grand Prix victories between 1994 and 2004.